Method of preparing a cracking or reforming feed stock



Patented Nov. 28, 1950 METHOD OF PREPARING A CRACKING OR REFORMING FEED STOCK John Watson Teter, Chicago, 111., assignor to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application June 21, 1947, Serial No. 756,314

2 Claims. 1

This invention relates to improvements in the production of motor fuels, particularly high octane gasoline, from hydrocarbon oils, in particular, petroleum.

In thermal and catalytic cracking operations for the production of motor fuels, it is recognized that aromatic compounds present in the feed stock are not cracked to an extent which involves scission or rupture of the aromatic rings, although side chains or the like may be split off. Further, there is a good deal of evidence to indicate that one of the major difliculties encountered in both thermal and catalytic cracking or reforming operations, namely, the formation of tar and/or carbon results from ring condensation of aromatic compounds present in the stock with the production of heavy materials. Substantially all the crude oils available contain substantial proportions of aromatic components. No effective way to separate the aromatic compounds from the aliphatic and naphthenic constituents of such oils has yet been described, and despite the fact that there has been recognition of possible improvement in cracking operations by separation of aromatic constituents from the charging stock no practicable means of accomplishing this result has been described.

The present invention provides a process by which the aromatic compounds present in the oil are subjected to ring scission before the stock is introduced into the cracking operation, with the result that the feed stock is largely dearomatized. The process results in an increased olefin content of the feed stock, which improves its cracking characteristics and the properties of the cracked motor fuel. Because of the great reduction in the aromatic content of the feed stock achieved by the process, the difliculties encountered both in thermal and catalytic cracking operations or reforming operations incident to the formation of carbon and tar are reduced.

In accordance with the present invention, the cracking feed stock is subjected to treatment with fluorine, and subsequently dehydrofiuorinated. The treatment with fluorine results in preferential reaction of the fluorine with the aromatic compounds present in the hydrocarbon stock, and in their conversion from aromatic compounds to unsaturated open chain compounds, which are highly oleflnic, and may even be acetylenic.

The reaction of the fluorine with the hydro carbon is highly exothermic. It must be carefully controlled, and the temperature must be held down, by supplying effective cooling to the reaction zone. The reaction temperature is relatively low for example, about 50 C. and not in excess of 300 C. Low pressures are used, for example, atmospheric pressure. The fluorine should be used in diluted form, for example, in admixture with carbon dioxide or nitrogen or mixtures thereof or other inert gases, and the fluorine content of the mixture should be relatively low, for example, about 10%. The reaction may be conveniently carried out by passing the diluted fluorine and the oil to be dearomatized countercurrently through a tower packed with a suitable material, for example copper Raschig rings or saddles.

The reaction of the hydrocarbon with the fluorine results in the production of a small proportion of saturated fluorocarbons, with all of the hydrogen replaced by fluorine, and these relatively inert materials should be removed from the oil before subjecting it to defiuorination. This is readily accomplished by fractionation in view of the relatively low boiling points of the fluorocarbons formed. The resulting product is then subjected to dehydrofluorination as by bringing it into intimate contact with bauxite or bauxite admixed with lime, in a tower, with splitting off of hydrogen fluoride and production of a hydrocarbon product substantially free from fluorine, of a highly olefinic nature, and with a greatly decreased aromatic content as compared with the initial stock. This product may be used as feed stock to a catalytic or thermal cracker. The lighter fraction for example, the C8 and lighter fraction may be subjected to hydroforming, or in View of the highly oleflnic nature of the material, it may be advantageously subjected to cracking or reforming in the presence of carbon monoxide and hydrogen as described in my application Serial No. 754,083, filed June 11, 1947.

The invention will be further described in connection with the appended flow sheet, which illustrates one form of apparatus in which the process may be carried out.

In the apparatus illustrated there is provided a reaction chamber I 0, packed with copper Raschig rings, designed to operate at atmospheric pressure and at a temperature of about 100 C. Banks of cooling coils are provided in the vessel to assist in maintaining the proper temperature, and remove heat formed by the highly exothermic reaction.

A recycle cracking stock, having a substantial aromatic content. is supplied to the top of the tower and passes downwardly through it. A

mixture of 10% fluorine with 90% inert gas is supplied to the tower at spaced intervals, to prevent too great a concentration of fluorine at any given level. The amount of fluorine so supplied is about 10% or less of that required for the complete fluorination of the stock, and will usually be of the order of about The fluorinated product is removed from the bottom of the tower and fed to the fractionating column 14 in which fiuorocarbons (CnFn+ 2) which may approach of the quantity of the stock in volume are taken as overhead product, with the remainder being taken as a bottoms product. This bottoms product is led through the preheater i0 and then fed to a tower l3 packed with a mixture of bauxite and lime maintained at a temperature between about 150 and 750 F. advantageously around 350 F. In this tower any fluorine compounds are dehydrofiuorinated with the hydrogen fluoride formed being either absorbed by the lime or passing oif as an overhead product, while the oil removed from the bottom of the tower is substanfia l fluori free, onmmatie n a a W an highly le n c cl im 1 In th r aration o dr rbon e s cks for c kin o eformin h prccess h ch omp i at n he fee s o k me n ar ma c con i u n with l ine #9 cause se sio o the ar ma in cem w ds be al pha ic compo nd se ara n s urat fl orocarbons and subjecting the product from h ch t fl oea bens have b en separ d to dehydrofluorinating treatment to obtain a cracking feed stock substantially free from fluorine h a rea l reduc d amm s o t- 4 ing a hydrocarbon feed stock containing aromatic constituents, the process which includes passing fluorine gas, diluted with an inert gas to a concentration of about 10%, in contact with the stock in a reaction zone, while cooling the reaction zone to maintain a temperature therein not in excess of 300 F., fractionating the resultant stool; to separate saturated fluorocarbons, dehydrofiuorinating the fluorinated hydrocarbons present in the stock from which the saturated fluorocarbons have been separated, by passing the stop}; in contact with bauxite at a temperature of to 750 F. to obtain a cracking feed stock substantially free from fluorine and with reduged aromatic content.

JOHN WATSON TE'IER.

REFERENCES CITED The following references are of record in the OTHER REFERENCES Fukuhara et al.: The Action of Elementary Fluorine upon Organic Compounds," Jour. Amer. Chem. Soc'., vol. 63, pages 2792 to 2795 (1941). 

1. IN THE PREPARATION OF HYDROCARBON FEED STOCKS FOR CRACKING OR REFORMING THE PROCESS WHICH COMPRISES TREATING THE FEED STOCK CONTAINING AROMATIC CONSTITUENTS WITH FLUORINE TO CAUSE SCISSION OF THE AROMATIC RING COMPOUNDS TO ALPHATIC COMPOUNDS, SEPARATIG SATURATED FLUOROCARBONS AND SUBJECTING THE PRODUCT FROM WHICH THE FLUOROCARBONS HAVE BEEN SEPARATED TO A DEHYDROFLUORINA;TING TREATMENT TO OBTAIN CRACKING FEED STOCK SUBSTANTIALLY FREE FROM FLUORINE AND WITH A GREATLY REDUCED AROMATIC CONTENT. 